(Adapted from Applicant's Abstract) Despite continued improvement in the technical aspects of cardiopulmonary bypass procedures, a majority of cardiac surgical patients demonstrate postoperative cognitive deficits and three per cent actually suffer frank strokes. Although it is not yet proven, the majority of researchers believe that these deficits are caused by emboli. In order to directly correlate the occurrence of neurologic and neuropsychologic deficits with intraoperative cerebral embolic events, it is essential to be able to measure the occurrence of emboli traveling toward the brain. The applicants propose a practical, cost effective instrument which will be able to intraoperatively monitor emboli. To achieve this goal, the applicants propose to design a specialized ultrasonic detector which will have a very large effective field of view. By this approach, the measuring probe can be positioned against the patient and continuously monitor the emboli count without the constant attention of a skilled operator. The development of this new emboli monitoring capability will be an important advancement in the understanding of the causes of neurological deficits related to cardiac surgery. It should allow critical interventions to be made in a timely manner and significantly improve the outcome of many patients undergoing cardiopulmonary bypass.